F. Volpe , M.E. Austin , G. Campbell , T. Deterly...Summary and Conclusions • Physical principle – Oblique ECE tracks island along ECCD line of sight, toroidally shifted – Signals

HTPD Monterey, CA 7-11 May 2012 F.Volpe 1

F. Volpe1, M.E. Austin2, G. Campbell3, T. Deterly3

1 Columbia University, New York2 University of Texas, Austin3 General Atomics, San Diego

Oblique-ECE Radial and Phase Detector of Rotating Magnetic Islands applied

to Alignment and Phase-locked Modulation of ECCD for NTM Stabilization

19th Topical Conference

High-Temperature Plasma Diagnostics

Monterey, CA, May 6-10, 2012

Yosemite, Sept.2006


Abstract

A 2 channel oblique Electron Cyclotron Emission (ECE) radiometerinterfaced to 4 gyrotrons was used at DIII-D to toroidally and radiallylocalize rotating magnetic islands and so assist their Electron CyclotronCurrent Drive (ECCD) stabilization. In particular, after manipulationsoperated by the interfacing analogue circuit, the oblique ECE signalsdirectly modulated the current drive in synch with the island rotation and inphase with the island O-point, for a more efficient stabilization. Apart fromthe different toroidal location, the diagnostic view was identical to theECCD launch direction, which greatly simplified the use in real time of thesignals. In fact, a simple toroidal extrapolation was sufficient to lock theECCD modulation to the O-point phase. This was accomplished by aspecially designed phase-shifter of flat response over the 1-7kHz range.Moreover, correlation analysis of two oblique ECE channels slightly aboveand below the ECCD frequency permitted to check the radial alignment ofECCD to the island, based on the fact that for satisfactory alignment thetwo oblique ECE signals must be out of phase.


Why modulating ECCD?

To maximize CD in the island (stabilizing) vs. CD outside (destab.)

For fairly oblique (Doppler-broadened), staggered launch of gyrotron beams, AUG and DIII-D can reproduce ITER-like conditions: w< dECCD

(narrow CD)

(broad CD)

dECCD


Why ECE (and not magnetic probes)?Because it is local toroidal phase & radial localization

• Mirnov:

++ Frequency

• ECE:

+ Frequency

0.0 0.2 0.4 0.6 0.8 1.0time (ms) – 4550.

• Mirnov:++ Frequency

+ Phase (measurement not local,

requires helical extrapolation)

−− Radial alignment

• ECE:+ Frequency

++ Phase (local but, if not in situ,

requires helical extrapolation)

++ Radial alignmentT

e(k

eV

) B

p(a

.u.)

MIRNOV

ECE 86.5GHz

125658

M.Marascheck et al. PRL 2007

rotation


Oblique ECE, along same direction as ECCD no equilibrium or other analysis required

• Island transit measured ‘in situ’

– same R, z of CD

– from same R, z of ECRH launcher

– with same pol. & tor. view angles

• Hence

– same relativistic downshift

– same relativistic & Doppler broadening

– island centre emits at f=fgyr=110GHz

• No need for FFT

• No need for flux surface shape

or helical extrapolations in R,z,f.

Extrapolation only in f.

• Horizontal ECE at 110GHz suffers from 3rd harm.

problems for BT<1.65T, oblique ECE only BT<1.55T

#125476

t=3750ms

B= -1.7T

#122898

t=5000ms

B= -1.5T


Oblique ECE from rotating island collected by transmission line 5

Modulated ECCD injected from lines 2, 3, 4 & 6 to stabilize island

fECCD ≠ fgyr but Df =15, 30, 330, 345o anyway


Island separatrix is an isothermal.

Signals on island sides are out-of-phase.

dTe in counter-phase

Same Te

(changes with time)Loc

Max

Loc

min

r3/2

MSE

0 0.5 1.0 r

4

2

0

Te(keV)


Two ECE channels close to island are sufficient to

track its rotation and radially localize it w.r.t. ECCD

ECE @ outer edge of island

ECE @ inner edge of island

Diff. of two horiz. ECE channels

MECCD w/form (apart from phase)

r 86.5GHz

88.5GHz

Mirnov

MECCD w/form (apart from phase)


Channels on opposite sides of island (mid-frequency aligned) out-of-phase

Channels on same side (mid-frequency misaligned) in phase

r 88.5GHz

90.5GHz

85.5GHz

87.5GHz


Oblique ECE as a waveform generator for modulated ECCD,

radially aligned, in synch and in phase with island O-point

Doppler-broadened,

relativistically shifted

111.5 108.5GHz ECRs

RM FiltersSubtractor/

Comparator

V1

V2

Analog Processing Freq & Phase of Modulation

Optical

Isolator

fibrePS Gyrotron

Optical

Isolator

fibrePS Gyrotron

Optical

Isolator

fibrePS Gyrotron

+Df

+Df

PCS

Digital Processing Radius of CD

(if wrong, move plasma or ECR)


Dichroic plate and plate array

Frequency selectivity

(no mix-up with LFS)

Modal Purity

(no mix-up with O-mode)


Analogue circuit modulates ECCD based on oblique ECE

and corrects phase for different toroidal location

Subtractor ComparatorPhase

ShifterV1-V2

V1

V2

300Hz < f < 20kHz

FilterV1-V2

• Phase shifters usually provide fixed time delay

• Special design: flat frequency response in phase

Frequency

to Voltage

Converter

Programmable

Voltage Controlled

Resistor

V

f

R 1/V 1/f

Dt=RC 1/f

but Df=const.

200

400

600

800

1000

0 2 4 6 8

f (kHz)

D

Df d

Dt (s)

Df (deg)


Gyrotrons are modulated at up to 10kHz

Balanced NBI slows down rotation to ITER-like valuesP

EC

RH(M

W)

f=10kHz

f=2kHz

time (s)

25

20

15

10

5

01.8 2.62.2 3.0 3.4 3.8

3/2, 4kHz

f (k

Hz)


Observed Phase Reversal, indication of good alignment !


Complete suppression of 3/2 by ECCD modulated

in phase with O-point !


Complete suppression of 3/2

is well separated from appearance of 2/1


Summary and Conclusions

• Physical principle

– Oblique ECE tracks island along ECCD line of sight, toroidally shifted

– Signals directly modulate ECCD

– Radial alignment in real-time, from 2 channel anti-correlation

• Demonstrated both techniques!

1. Observed “Phase-reversal”, indication of good alignment

• confirmed by 3/2 stabilization and by equilibrium and ray tracing

analysis

2. 3/2 NTM completely suppressed by ECCD modulated in phase

with O-point on the basis of oblique ECE signals


Future Works

• Stabilize 2/1

• Align in real-time

• Compare with Mirnov

• Oblique radiometer might also serve to:

– EBW emission

– Collective Thomson Scattering

– Correlation with horizontal ECE ( toroidal mode number)

– Positron Cyclotron Emission

• Electronics can be used with any NTM diagnostic

Documents

F. Volpe , M.E. Austin , G. Campbell , T. Deterly...Summary and Conclusions • Physical principle – Oblique ECE tracks island along ECCD line of sight, toroidally shifted – Signals